With the advent of substantial new uses for high bandwidth digital and analog optical systems, there exists a greater need to effectively control the route of optical beams from among many possible paths. This is especially true in digital computing systems where signals must be routed among processors, in analog systems such as phased array radar, and in the switching of high bandwidth optical carriers in communication systems. However, it should be realized that these are just several of numerous systems that require the use of an optical switching or routing mechanism.
In many current and future systems light beams are modulated in a digital and/or analog fashion and are used as “optical carriers” of information. There are many reasons why light beams or optical carriers are preferred in these applications. For example, as the data rate required of such channels increases, the high optical frequencies provide a tremendous improvement in available bandwidth over conventional electrical channels such as formed by wires and coaxial cables. In addition, the energy required to drive and carry high bandwidth signals can be reduced at optical frequencies. Further, optical channels, even those propagating in free space (without waveguides such as optical fibers) can be packed closely and even intersect in space with greatly reduced crosstalk between channels. Finally, operations that are difficult to perform in the lower (e.g., radio) frequencies such as time shifting for phased array applications can often be performed more efficiently and compactly using optical carriers.
A common problem encountered in applications in which high data rate information is modulated on optical carrier beams is the switching of the optical carriers from among an array of channels. These differing optical channels may represent, for example, routes to different processors, receiver locations, or antenna element modules. One approach to accomplish this switching is to extract the information from the optical carrier, use conventional electronic switches, and then re-modulate an optical carrier in the desired channel. However, from noise, space, and cost perspectives it is more desirable to directly switch the route of the optical carrier from the input channel to the desired channel, without converting to and from the electronic (or microwave) regimes.
Another common problem arises in applications where there is a need to arbitrarily interconnect any of n electronic input channels to any of n output channels. This “crossbar switch” type of function is difficult to implement electronically. In such a case better performance may be obtained by modulating the electronic information on optical carriers, and switching the optical carriers to the desired channel where they may be reconverted to electronic information if desired. This conversion to optical carriers permits the use of optical switching techniques as in the present invention, as well as providing a ready interface to other optical interconnect schemes.
Another problem that is typical in optical switching systems is the insertion loss they impose. Some switching systems divide the input signal power into many parts, and block (absorb) the ones that are not desired. Others use switches that are inefficient and absorb or divert a significant part of the input signal.
The optical switching and routing systems of U.S. Pat. No. 5,771,320 (issued to T. W. Stone on Jun. 23, 1998), incorporated by reference herein, overcame some of the problems associated with complexity and performance, including number of required switching devices and control signals, switch isolation, noise and crosstalk suppression, insertion loss, spurious reflections, data skew, and compactness that were present in preceding optical switching systems.
One optical switching and routing system described in U.S. Pat. No. 5,771,320 utilizes a pair of router assemblies made up of a series of switchable diffraction gratings. The second router assembly is crossed in orientation with respect to the first router assembly. In one embodiment, the switchable diffraction gratings are polarization selective gratings. Such switchable polarization selective gratings typically transmit light of a first polarization in both the switched states and diffract light of a second distinct polarization in one switched state, and transmit light of the second distinct polarization in the other switched state.
In the type of switching and routing systems utilizing switchable polarization selective gratings, there is a need for improved coupling between the first and second router assemblies.
Further, in the type of switching and routing systems utilizing switchable polarization selective gratings, there is also a need for polarization insensitive switching and routing systems.
It is one object of this invention to provide polarization selective switching and routing systems with effective coupling between the first and second router assemblies.
It is another object of this invention to provide systems and methods for polarization insensitive switching and routing.
It is yet another object of this invention to provide optical systems and methods that can be utilized in polarization insensitive switching and routing systems.